Monday, Nov 2, 2009 - 3A

Collected Ball and Ramp Labs
Handed back Act-A-Graph HW

Asked if any questions on Act-A-Graph HW
Asked what curve students got from Ball and Ramp Lab and what it indicates.

Curve shows the ball starts off slow and gradually speeds up. The control in a car that allows you to speed up is the gas pedal or accelerator. You are changing your speed, you are accelerating.

You accelerate when you change your velocity in a given time interval. There are three ways in which you can change your velocity - speed up, slow down, change direction.

Demo with Intel man and Jeep Rubicon. You can feel acceleration. Demo with car trip - you can feel acceleration. In Oaks Park on the Roller Coaster, as it suddenly dips, your body is down but your stomach is up - you feel acceleration. You cannot feel constant velocity. Suppose student wins all expense paid trip to Europe. On 747, plane is traveling at 1000 km/hr. If there is no turbulence, you cannot feel the motion.

Examples with money. Amount earned is pay rate * time
Amount you have = amount you started with + amount earned = amount you start with + pay rate * time. Did several examples.
Suppose you get a pay raise. In the second year you earn $12/hr and in the third year you earn $14/hr. Your pay rate is increasing at a rate of $2/hr/year. There are two time terms since this is the rate of a rate. This is not your pay rate, it tell you how your pay rate is changing. Analogy with velocity and acceleration. How fast you are going = how fast you started + acceleration * time

Acceleration is defined as the change in velocity in a time interval, a = (vf-vi)/t

Velocity is the rate at which you cover distance in a particular direction. It is how fast you are going in a particular direction. Acceleration is the rate of a rate, the rate at which velocity changes.

Did examples with cars speeding up and slowing down. Did examples of finding acceleration and also finding how fast after a given time.

You can be moving but not accelerating (if you are moving at a constant velocity). You can be accelerating if you are not moving. (Move ruler in ball and lamp lab to release ball. If there were no acceleration, it wouldn't change how its moving so it would stay still. Throw a ball up into the air. On the way up it slows down. At its highest point it is momentarily at rest, but the acceleration is NOT zero. It the acceleration were zero, it would just hover in the air since it would not change how it's moving.

The ball and ramp lab showed the ball accelerated (sped up) down the ramp. When you drop a ball, it also speeds up on the way down.

Did Picket Fence Lab to show students how to use the computers and how to determine the acceleration of gravity. Students got values around 9.7 m/s/s. The generally accepted value is about 9.8 m/s/s at the surface of the Earth. We will round this to 10 m/s/s. This makes it particularly easy to determine how fast a ball is moving after falling for a given time. vf = vi + a * t

Did several examples with dropping a ball, throwing a ball down, and even throwing a ball up.

Homework - RA 1.2
Also can do CD
Also try Quia for motion graphs, activities, and acceleration quizzes.